1. Field of the Invention
The present invention relates to a circuit breaker, and more particularly to a circuit breaker to automatically interrupt the electricity supply when the current flow exceeds a predetermined level.
2. Description of Related Art
To protect electrical equipment, a circuit breaker is generally used to automatically discontinue the electricity supply when the device abnormally starts to draw an excessive amount of electricity, which is so called over current.
With reference to FIG. 5, a conventional circuit breaker includes a housing (70) arranged with two conductive plates (71) (72), wherein a bimetallic strip (73) is connected to one conductive plate (72). The bimetallic strip (73) has a tongue portion (74) to which a movable node (76) is mounted. An immovable node (75) is secured at one end of the other plate (71) to correspondingly contact the movable node (76).
A movable arm (77) and a plate (79) are placed inside the housing (70). The movable arm (77) has two ends from which a lateral portion (770) and an upward partition plate (78) are respectively extended. A spring (82) retained in the housing (70) abuts against a lower edge of the lateral portion (770) of the movable arm (77). The plate (79) has a foot portion (80) protruding from the bottom edge of the plate (79). A switch (81) is pivoted to a stub (not numbered) protruded from the housing (70). The bottom portion of the switch (81) touches the lateral portion (770) of the movable arm (77) and a top point of the plate (79) as shown in FIGS. 6 to 8.
With reference to FIG. 6, when a current flowing through the two conductive plates (71)(72) increases abnormally, the bimetallic strip (73) becomes hot and deforms. The spring (82) will push the lateral portion (770) upward so that the switch (81) is switched toward one side (the left side on the drawing). Because the movable arm (77) is pushed upward by the spring (82), the partition plate (78) accordingly moves upward at a position between the movable node (76) and the immovable node (75) thus separating them from each other.
With reference to FIG. 7, by pressing the switch (81), the lateral portion (770) of the movable arm (77) is pressed downward and thus the partition plate (78) moves downward also, whereby the movable node (76) and the immovable node (75) will contact each other.
To terminate the electricity supply by human force, the plate (79) is moved downward by pressing the switch (81) thus allowing the foot portion (80) to move the tongue portion (74) away to separate the movable node (76) from the immovable node (75). Meanwhile, because the switch (81) has been switched toward the left side, the compressed spring (80) turns to the released status and pushes the lateral portion (770) upward. Therefore, the partition plate (78) is located between the movable node (76) and the immovable node (75).
With reference to FIG. 8, if the pressing force applied on the switch (81) is not strong enough, the movable arm (77) is just at the middle position and the spring (82) is unable to push the movable arm (77) upward. The movable node (76) and the immovable node (75) become very close but do not contact each other, so that a possible electric arc with extremely high temperature may take place and damage the two nodes (75)(76).